1. Field of the Invention
The present invention relates to a receiving method and a receiving apparatus for estimating the received signal quality, and a communication system using the receiving apparatus.
2. Description of the Prior Art
Various technologies are introduced to conventional communication systems, in particular, a radio communication system, for the purpose of the high efficiency of a transfer method and the increase in transfer capacity. For example, the abovementioned technologies include a multivalue modulating technology, e.g., a quadrature amplitude modulating (QAM) method serving as a modulating method, an orthogonal frequency division multiplexing (OFDM) method serving as a multiplexing method, punctured convolution coding which is obtained by combining convolution coding and punctured processing serving as codec processing, and turbo coding, and the like. Further, one of the abovementioned conventional technologies is disclosed in a book titled “WAVE SUMMIT COURSE (Ido Tsushin in Japanese)” written and edited by SASAOKA Shuichi and published by Ohmsha, Ltd. on Mar. 25, 1998.
Hereinbelow, a description is given of an example of the configuration and the operation of a receiving station in the conventional high-efficient communication system with reference to FIG. 1. Here, it is assumed to use the punctured convolution coding as the codec processing, a 64-level QAM method whereby the signal point is arranged by a gray code as the modulating method, and the OFDM as the modulating method. A signal transmitted from a transmitting station 10 is subjected to the to the orthogonal frequency division multiplexing, and the resultant signal is received and demodulated by an OFDM receiving unit 21. Consequently, a receiving station 20 obtains a modulating result every sub-carrier. A multivalue-QAM demodulating unit 22 performs the 64-level QAM demodulation processing of the sub-carriers, thereby obtaining a demodulating result. The transmitting station 10 performs the so-called punctured convolution coding processing of transmitting data, that is, deletes data at a predetermined position thereof. Then, in a codec unit 23, a de-puncturing processing portion 24 depunctures the data and thereafter a Viterbi decoding portion 25 Viterbi-decodes the data at the predetermined position which is subjected to the puncturing processing, thereby restoring the data transmitted from the transmitting station 10.
With the abovementioned configuration, the efficiency for frequency use is improved and the communication with a large capacity is possible between the transmitting station 10 and the receiving station 20.
When the communication capacity is highly efficient with the abovementioned configuration, various factors in the processing cause the communication quality to vary depending on the position of bit data in a frame. For example, the communication quality in the OFDM method varies depending on the position of the sub-carrier due to the property of a transmission path between the transmitting station 10 and the receiving station 20 and due to a deteriorating factor in an analog processing unit for filter processing and the like in the transmitting station 10 and the receiving station 20. Further, since the average distance between signal points of bits is essentially different in the reception and demodulation of the 64-level QAM with the arrangement of the signal points shown in FIG. 4, the obtained communication quality varies. Specifically, it is known that the qualities of bits b0 and b1 are the highest and the qualities of bits b4 and b5 are the lowers. Further, it is generally well-known that data is subjected to the interpolation processing of phase and amplitude by use of a previously-inserted well-known pilot symbol in the QAM demodulation and the data is subjected to the compensation of phase and amplitude. However, the symbol apart from the pilot symbol is not fully interpolated and the quality might deteriorate depending on the precision of interpolation processing. Further, a code through the punctured convolution coding might essentially vary the distance between the codes.
As mentioned above, since the communication quality might vary in the processing units, the communication qualities at the positions in a finally-obtained received data frame are not uniform and are varied. Generally, in order to reduce the variation in communication quality, the codec processing unit makes the communication quality uniform by combining the interleave processing and the error correction in many cases.
As the data communication using the above high-efficient transfer method, recently, the data is communicated by increasing use of the packet transfer of an IP (Internet Protocol) and the transfer of multi-media as upgrade transfer thereof, e.g., a moving image, audio information, and text information with the large capacity. It is assumed that moving image data through the MPEG coding is transferred. A data sequence generated by the coding contains various header portions (a sequence header and a picture header) and image data. (DCT coding data portion). The degree of influence upon decoding the image varies depending on the portions of the data sequence when an error is caused upon communication. Specifically, the occurrence of communication error at the sequence header portion or the picture header potion influences the entire sequence block and picture header portion, thus excessively deteriorating the image quality. However, the occurrence of the communication error in a DCT encoding data unit doe not exert the influence only on the DCT block. The encoding processing uses a variable code and, therefore, the occurrence of the communication error at the header portion in the data sequence does not enable the decoding of the subsequent portions up to the position at which the next start position of the well-known variable code is inserted and this exerts the serious influence on the image reading. The above-generated data sequence includes many services in which the influence on the quality of the communication service varies depending on the component of the data sequence.
In transmitting the data with the large capacity, the data sequence generated by the updating processing is basically generated regardless of the transfer method of a physical layer. Further, the data sequence is generally supplied to a processing system of the physical layer by a fixing method in accordance with a predetermined procedure, and the procedure is not dynamically changed. In this case, upon transmitting MPEG moving image data, data in header information portions (sequence header, picture header, etc.) with high influence on the original image quality is fixedly allocated at the position with the low quality in the physical layer, and the image quality is not fully obtained.